This invention relates to apparatus for measuring the static cutter compliance of a machine tool.
It is generally desirable to operate numerically controlled machine tools and the like att the highest possible feed rate. The feed rate is often limited by the maximum force which the cutting edge of the cutting tool can apply to the work without causing breakage of the cutter. In finishing operations, the feedrate must also be maintained below a certain level to keep the surface roughness of the finished work surface below a predetermined level.
Direct measurement of the force on the cutting edge of the tool is desirable but not always attainable in practice. Instead of measuring force on the cutter, some machines measure deflection produced by the force on the cutter. Some machines have deflection sensors that measure the deflection of the spindle during cutting to limit the feed rate. In order to determine the force on the cutting tool with such sensors, it is necessary to determine the compliance of the spindle/tool system, or in other words, the relationship between the force on the cutting tool and the deflection sensed by the spindle deflection sensor. This relationship varies according to the particular cutter used, the method of cutter mounting on the spindle, the location and length therealong at which it contacts the work, and other factors. Thus, it is generally desirable to calibrate the compliance of the spindle apparatus for each particular cutting tool set-up.
The on-line calibration of compliance can be accomplished by applying a known force at a location on the machine system near the active region of the nonrotating cutter and measuring the spindle deflection. It is desirable that any such force-applying apparatus be accurate to at least a few percent, and that it retain such accuracy in spite of a relatively hostile environment encountered in actual usage, where dirt, oil, coolant, chips, and the like may be present and where the calibration apparatus may be subjected to rough handling.